1. Field of the Invention
Present invention relates to a sensitivity calibrating method for a detector of comparator, more specifically, it relates to a method for calibrating a sensitivity of a detector of a comparator for inspecting an object such as a gauge block.
2. Description of Related Art
(Comparator for gauge blocks etc.)
A comparator relating present invention in general employs "comparative measuring method" for confirming a dimension of an object, that is, such comparator measures a dimension of an object to be confirmed after acquiring reference value from a reference object as a master. In such a comparator, the objects are, for example, put on a table through holders or the like and moved to measure a plurality of objects successively. A spindle of a detector is moved in a detecting direction (an axial direction of the spindle, i.e. z-axis direction) against the moved object thereby abutting a probe provided at the tip end of the spindle, and a displacement (distance, height) of the probe from an upper surface of the table is detected.
Some of the objects to be measured by such a comparator are large in height on the table (that is, thick), and some of them are small (thin). And some of the thin objects are, for example, warped upward. In measuring such objects, measuring error is caused since the lower surface which should be in close contact with the table gets remote away from the table, thus failing in measuring with high-accuracy.
(Comparator with opposing detectors)
In order to prevent such measuring errors, a measuring method for a comparator conducting particularly accurate measurement has been developed conventionally, where another detector (second detector) with upwardly extending probe is provided inside the table as well as aforementioned upper detector (first detector), and measure the object by abutting probes on both upper and lower surface thereof.
In this method, even if the lower surface of the object is detached from the table, aforementioned errors can be prevented since the detached lower position is measured.
In such comparator with opposing two detector, width dimension of the object can also be measured by using a pair of detectors opposing in lateral direction.
(Problems in a comparator with opposing detectors)
Though highly accurately finished spindle or the like should be used for the detectors of aforementioned comparator, slight error is inevitably generated. Thus each of the upper and lower detectors has inherent errors thereof.
In order to maintain an accuracy of the comparator, sensitivity calibration is conducted for each detector as in the nature of things. However, since the sensitivity calibration is conducted based on compound values of measured value of both upper detector and lower detector, it is not clear whether the error of the comparator is caused by upper detector or lower detector.
Therefore, even if a certain error is perceived, it is difficult to determine which detector's sensitivity should be calibrated, which result in difficulty in conducting highly-accurate calibration.
A number of measurements are sometimes necessary to be repeated and confirmed of the accuracy thereof, in order to determine which detector has the error. Moreover, accurate sensitivity calibration has to be conducted thereafter.
An object of present invention is to provide a sensitivity calibration method for a detector of a comparator which enables easy and highly accurate sensitivity calibration for a first and a second detector for measuring an opposing position of an object.